Crude glycerol by transesterification process from used cooking oils: Characterization and potentialities on hydrogen bioproduction

Abstract

This study evaluated the potential bioconversion of crude glycerol from biodiesel production, applying used cooking oil for biohydrogen production by fermentative bacteria consortia. The pretreatment of crude glycerol was made by pH adjustment. Heat treatment of the inocula and initial pH 5.5 were applied to select hydrogen-producing bacteria and inactivate hydrogen-consumers microorganisms. The inocula tested were: (I) granular sludge from the thermophilic UASB reactor used on the treatment of vinasse and (II) granular sludge from the UASB reactor used on the treatment of sanitary sludge for the assays (1) and (2), respectively. The characterization of crude glycerol presented high levels of alkalinity, methanol and soap that may be inhibitory to biologic processes of H 2 production. The assays were carried in anaerobic batch reactors in order to verify the efficiencies of crude glycerol to H 2 generations by the microbial consortia (20%) at 37 C, initial pH 5.5, with 20.0 g COD L À1 glycerol. The cumulative production of hydrogen for the assays (1) and (2) were, respectively, (mmol H 2 L À1) 28.49 ± 1.55 and 19.14 ± 1.67. The subsequent yields were obtained as follows: 2.2 moL H 2 mol À1 glycerol and 1.1 moL H 2 mol À1 glycerol, respectively. The used cooking oil was an efficient waste for bioconversion of crude glycerol to H 2 production.

Bioconversion of crude glycerol from waste cooking oils into hydrogen by sub-tropical mixed and pure cultures

“…The COD values during the operation of the anaerobic batch reactors did not change significantly (COD initial 49.79 g COD L À1 and COD final 48.46 g COD L À1 for the mixed culture and 46.61 g COD L À1 initial and 42.58 g COD L À1 final for the pure culture). This fact can be explained by the glycerol metabolic pathway known for the fermentative H 2 -producing bacteria, suggesting that occur a transformation of the initial substrate into other volatile organic compounds, which remain in the liquid phase, causing the maintenance of COD throughout the assays [7].…”

“…According to Rodrigues et al (2016) [7], the WCO applied as a feedstock for the biodiesel production reduces the costs for this process of 60e70%. In São Paulo, Brazil, on March/April 2017, the WCO had price of R$1.00 per liter [8], while raw virgin of soybean oil price was R$2.57 per liter [9], a price of almost 2.6 more than WCO.…”

“…For this reason, the large quantities of crude glycerol produced each year have impacted the glycerol market, resulting in low prices of crude glycerol (1.54 US $/Kg before 2000 and 0.66 US $/Kg after 2007). Crude glycerol has been a financial and environmental liability of the biodiesel industry [7,13].…”

Evaluation of a Passive Anion‐Exchange Membrane Micro Fuel Cell Using Glycerol from Several Sources

“…The soap presented in the HPG, SPDG, CGSOB and CGCOB samples was in the form of as sodium oleate. The method used for measuring soap content consisted of mixing 10 g of the glycerol sample with a mixture of 60 mL of acetone and 0.15 mL of 0.5% w/v bromophenol blue, and then titrating the solution using a hydrochloric acid solution (0.1M) . Furthermore, volumetric Karl Fischer titrations were used to determine the water content in the glycerol samples.…”

“…The amounts of moisture and volatile matter in the glycerol samples were determined by AOCS Ca 2c‐25 . The amount of non‐glycerol organic matter was determined by centrifugation of the glycerol samples at 900 rpm for 10 min (pH 2.0) to separate all non‐glycerol organic matter .…”